This invention relates to methods and mold constructions for making molds of plastics, such as epoxy resin. These molds may be made by pouring uncured, liquid plastic epoxy resin over models in segmented shoes. The present invention is especially directed to the forming of epoxy resin molds for molding tires which have recesses in the tread surface which are formed by stand alone ribs in the surfaces of the molds. The segmented shoes are reusable and may be prefabricated with standard shoe split diameters and chord lengths to reduce the time necessary to make subsequent molds. Alignment and sealing of the shoe parts is provided.
As shown in U.S. Pat. No. 4,858,881, it has been proposed to make partial tire molds of epoxy or other resin to repair tire sidewalls. It has also been proposed to reinforce plastic articles with glass fibers, as shown in U.S. Pat. No. 4, 692,291. U.S. Pat. No. 5,449,483 uses modular shoe containers for making metal shells with a resin backing.
The transfer of metal blades from slits in a matrix of rubber to a mold shell is described in U.S. Pat. No. 2,275,582. The matrix is covered by an electro-formed metal shell which bonds to the blades so that upon removal of the matrix the blades become part of the metal mold shell. The mold shell must then be machined to become part of a tire mold.
In accordance with the method of this invention, a model of a segment of a tire having a tread configuration with recesses such as grooves, slots and slits in the model surface is mounted in a shoe having a chamber for receiving a plastic, such as uncured, liquid epoxy resin, to form a complete segment of the tire mold. Before filling the chamber with the uncured epoxy resin , the model is sprayed with a grease type spray release agent which does not react with the epoxy resin to retard its curing.
In one embodiment of this invention a mixture of fiberglass and epoxy is sprayed on the surface of the model and into the recesses in the model surface to provide reinforced stand alone ribs in the tread molding surface of the epoxy resin mold after curing and removal of the mold from the model. In another embodiment, the mixture of uncured epoxy resin and fiberglass is formed in a semi-liquid putty-like consistency, and instead of spraying, this material is packed against the surface of the model to fill the recesses in the model surface. After the recesses are filled by packing the mixture of epoxy resin and fiberglass and allowing it to cure the chamber in the shoe is completely filled by pouring uncured liquid epoxy resin mold material into the chamber of the shoe to form a complete mold segment. This liquid epoxy resin mold material is then cured.
In another embodiment, a slurry of liquid epoxy resin and fiberglass is poured directly over the model and the chamber filled after which pressure is applied to force the slurry into the recesses in the model surface and to form stand-alone ribs in the mold surface.
In a further embodiment, single or laminated metal blades are inserted in the slits of the model after the model has been sprayed with a release agent. The blades may be glued to the model with an appropriate adhesive for bonding metal to elastomeric materials. The model is then mounted in a shoe container and filled with a liquid epoxy resin mold material which bonds to the surface of the blades. The epoxy resin mold material is cured and then cooled. When the model is removed, the solidified epoxy resin mold material contained in the shoe is pulled away from the model. The blades remain in the epoxy tread mold and reinforce the ribs and make them capable of withstanding the stress and strain from the tire molding process.
The model is preferably a resilient elastomeric material facilitating insertion of the blades into the slits of the model and removal of the blades from the slits in the model after pouring of the epoxy resin mold material. The model can then be used again to form another tread mold segment.
The process of this invention provides steel or aluminum parts to make the epoxy resin tread mold segment and to hold the segments during tire curing. Parts of different sizes have been needed to make molds of different tire sizes. In order to make the molds quickly, the parts have been prefabricated. In accordance with this invention, the number of different size parts has been reduced by prefabricating them in different sizes using two dimensional standards. One dimensional standard is the mold split diameter which is the diameter at which the sidewall plates meet the tread segments. The other dimensional standard is the chord angle and the sequence of the slide block parts which are used in the mold mechanism.
The shoes of this invention may also be used more than once by providing a U-shaped cavity with radial sides permitting easy removal of the epoxy mold tread segment from the cavity after curing while at the same time the tread segment mold part is secured without requiring lips on the edges. This is accomplished while providing sealing of the shoe cavity and holding the model bracket in alignment with the shoe.
In accordance with one aspect of the invention, there is provided a method of providing reinforced stand-alone ribs in the molding surface of a mold of epoxy resin mold material for molding an article having recesses in the surface comprising:
(a) making a model of elastomeric material having recesses in the surface of the model;
(b) applying a release agent to the surface of the model characterized by;
(c) inserting metal blades in the recesses;
(d) placing the model in a shoe container chamber having the shape of a complete mold part;
(e) filling the shoe container chamber with an epoxy mold material to form a complete mold part;
(f) curing the epoxy mold material in the container while it is cured to form the mold part; and
(g) separating the mold part from the model with the metal blades adhering to the mold part and being pulled out of the recesses in the surface of the model.
In accordance with another aspect of this invention, there is provided a method of providing reinforced stand-alone ribs in the surface of a plastic mold for molding an article having recesses in the surface of the article comprising
(a) making a model of elastomeric material having recesses in the surface of the article;
(b) applying a release agent to the surface of the model characterized by;
(c) spraying the surface with uncured epoxy resin mold material containing reinforcing material to fill the recesses;
(d) placing the model in a shoe container chamber having the shape of a complete mold part;
(e) filling the shoe container chamber with the uncured epoxy resin mold material to form a complete mold part;
(f) retaining the epoxy resin mold material in the container chamber while it is cured to form the mold part; and
(g) separating the mold part from the model with the epoxy resin mold material in the recesses being pulled out of the recesses in the model in the form of stand alone ribs.
In accordance with a further aspect of this invention, there is provided a method of providing reinforced stand alone ribs in the surface of a plastic mold for molding an article having recesses in the surface of the article comprising
(a) making a model of elastomeric material having recesses in the surface of the model;
(b) applying a release agent to the surface of the model characterized by;
(c) packing plastic mold material containing reinforcing material against the surface and into the recesses of the model;
(d) placing the model in a shoe container chamber having the shape of a complete mold part;
(e) filling the shoe container with a plastic mold material to form a complete mold part;
(f) retaining the plastic mold material in the container while it is cured; and
(g) separating the mold part from the model with the plastic mold material containing the reinforcing material in the recesses being pulled out of the recesses in the model in the form of reinforced stand alone ribs.
In accordance with a still further aspect of the invention there is provided a tire mold comprising:
(a) a plurality of mold segments of epoxy resin mold material;
(b) each of the segments having a radially inner tread molding surface with ribs for molding recesses in the tread surface characterized by;
(c) the tread molding surface having stand alone ribs of a mixture of epoxy mold material and reinforcing material; and
(d) each of the mold segments being completely shaped to mold a segment of a tire tread in the tire mold.
In accordance with another aspect of the invention there is provided a complete tire mold comprising:
(a) a plurality of mold segments of epoxy resin mold material;
(b) each of the segments having a radially inner tread molding surface with metal blades adhered to the segment for forming recesses in a tire made by the mold.
(c) a segmental shoe of metal encasing each of the mold segments of epoxy resin material comprising;
(d) radially extending shoe side plates providing a U-shaped cross section in a radial plane containing the axis of the mold whereby after use of the segmental shoe, the epoxy mold material may be removed from the chamber of the segmental shoe of metal so that the shoe may be used again;